The present invention relates generally to ophthalmic compositions. In particular, the present invention relates to the use of certain anionic surfactants, particularly modified sarcosinates and lactylates, to prevent or to reduce binding of the antimicrobial components of ophthalmic compositions to other components contained therein, thereby improving the antimicrobial efficacy of such compositions.
In recent years, a number of ophthalmic compositions have been introduced which contain a variety of components, such as carboxyvinyl polymers (e.g., Carbopol.RTM.), ion exchange resins (e.g., Amberlite.RTM.), or other large polyelectrolytes, which provide sustained release of the ophthalmic agent(s), as well as increased patient comfort. Such compositions are described, for example, in U.S. Pat. No. 4,911,920 (Jani et al.). Although these compositions are comfortable and have sustained release characteristics, cationic antimicrobials, such as benzalkonium chloride (BAC), which are often added as preservatives to such compositions tend to bind to the anionic molecules present in the formulations, resulting in loss of antimicrobial effectiveness.
Sarcosinate surfactants are composed of acylated sarcosines. Sarcosine (CH.sub.3 --NH--CH.sub.2 --COOH) is an amino acid derivative produced in the body for the synthesis of glycine (NH.sub.2 --CH.sub.2 --COOH), a basic amino acid. Common fatty acids and their derivatives utilized in the manufacture of sarcosinate surfactants are lauric, oleic, and myristic acids and their esters and halides. Because of their mildness, sarcosinate surfactants have been utilized in shampoos, mouthwashes, skin cleansers, sunscreens, aerosol shaving lathers and other personal care products. To date, the main applications of these types of surfactants have been in the cosmetic industry. For example, European Patent 194097 (Schmidt et al.), assigned to Procter & Gamble, mentions sodium lauroyl sarcosinate as the mild anionic surfactant utilized in an aerosol skin-cleansing and moisturizer mousse. Applicants are not aware of any ophthalmic use of these types of surfactants.